Over 100,000 PTFE graft angioplasties are performed in America each year to restore adequate access flow, but up to 50% of the procedures must be repeated within three months. Radiologist now derive interventional efficacy from pressure and vessel diameter measurements. Direct measurement of volume flow (ml/min) would give immediate feedback on procedural success. Transonic Systems proposes to resolve this need by further developing and commercializing an inexpensive catheter-based AngioFlowmeter for measuring blood flow during angioplasty of PTFE grafts and native fistulae. Our Phase-I clinical studies demonstrated that access flow may be measured accurately and repeatably using thermodilution catheters introduced through the angioplasty antegrade sheath and room temperature saline injections. Our Phase-ll plans are to: Attain FDA clearance. Refine and validate the catheter designs and measurement algorithms for catheter placement through antegrade and retrograde introducer sheaths; Refine and validate algorithms to identify whether the flow-limiting stenosis is on the graft arterial or venous side; Demonstrate the system's efficacy in controlled clinical trials; Publish results of the study in preparation for market introduction. At the end of Phase II, Transonic Systems aims to market the AngioFlowmeter as a new quality assurance tool for interventional radiology procedures. PROPOSED COMMERCIAL APPLICATION: An access flow measurement catheter would have routine use during radiological and surgical interventions to restore flow. It would allow quantitative assessment of the efficacy of percutaneous angioplasty and thus support improved outcomes. This may in turn reduce the need for repeat interventions, improve the quality of life for ESRD patients, and reduce healthcare costs in the US by $18 million/year. We aim to market this device to surgical and interventional radiology and interventional radiology suites worldwide.